Near-Equilibrium Solubility of Nanocrystalline Alloys

2012 ◽  
Vol 1371 ◽  
Author(s):  
Alexander Kirchner ◽  
Thomas Riedl ◽  
Konrad Eymann ◽  
Michael Noethe ◽  
Bernd Kieback
Keyword(s):  
Grain Boundaries ◽  
Nanocrystalline Materials ◽  
Excess Volume ◽  
Boundary Segregation ◽  
Equilibrium Solubility ◽  
Equilibrium Conditions ◽  
Common System ◽  
Proposed Model ◽  
Materials Behavior ◽  
Atomistic Computer Simulation

ABSTRACTGrain boundaries are the dominating type of defect in nanocrystalline materials. Understanding their properties is crucial to the comprehension of nanocrystalline materials behavior. A facile thermodynamic model for alloy grain boundaries is developed. The macroscopic analysis is based on established descriptions of metallic solutions and the universal equation of state at negative pressure, using mainly parameters obtainable from measurements on macroscopic samples. The free energy of atoms in grain boundaries is derived as a function of excess volume, composition, and temperature. Interfacial enrichment is computed using equilibrium conditions between bulk phase and grain boundaries. The excess volume of symmetric ‘100’ tilt grain boundaries in Cu as a common system is obtained by atomistic computer simulation. In a general case the predictions of the proposed model are compared to experimental grain boundary segregation data, yielding a good match. The near-equilibrium solubility of Ag in nanocrystalline Cu and of Cu in nanocrystalline Fe is calculated.

Grain boundary segregation in metals

1992 ◽  
Vol 50 (2) ◽  
pp. 1204-1205
Author(s):  
C.L. Briant
Keyword(s):  
Fracture Surface ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Material Properties ◽  
Electron Spectroscopy ◽  
High Vacuum ◽  
Boundary Segregation ◽  
Grain Boundary Segregation ◽  
Local Concentration ◽  
The One

Grain boundary segregation is the process by which solute elements in a material diffuse to the grain boundaries, become trapped there, and increase their local concentration at the boundary over that in the bulk. As a result of this process this local concentration of the segregant at the grain boundary can be many orders of magnitude greater than the bulk concentration of the segregant. The importance of this problem lies in the fact that grain boundary segregation can affect many material properties such as fracture, corrosion, and grain growth.One of the best ways to study grain boundary segregation is with Auger electron spectroscopy. This spectroscopy is an extremely surface sensitive technique. When it is used to study grain boundary segregation the sample must first be fractured intergranularly in the high vacuum spectrometer. This fracture surface is then the one that is analyzed. The development of scanning Auger spectrometers have allowed researchers to first image the fracture surface that is created and then to perform analyses on individual grain boundaries.

EELS Measurement of the Local Electronic Structure of Copper Atoms Segregated to Aluminum Grain Boundaries

1996 ◽  
Vol 54 ◽  
pp. 342-343
Author(s):  
S.J. Splinter ◽  
J. Bruley ◽  
P.E. Batson ◽  
D.A. Smith ◽  
R. Rosenberg
Keyword(s):  
Electronic Structure ◽  
Grain Boundaries ◽  
Boundary Segregation ◽  
Thin Layers ◽  
Nominal Composition ◽  
Spatially Resolved ◽  
Service Lifetime ◽  
Heat Treated ◽  
Probe Size ◽  
Local Electronic Structure

It has long been known that the addition of Cu to Al interconnects improves the resistance to electromigration failure. It is generally accepted that this improvement is the result of Cu segregation to Al grain boundaries. The exact mechanism by which segregated Cu increases service lifetime is not understood, although it has been suggested that the formation of thin layers of θ-CuA12 (or some metastable substoichiometric precursor, θ’ or θ”) at the boundaries may be necessary. This paper reports measurements of the local electronic structure of Cu atoms segregated to Al grain boundaries using spatially resolved EELS in a UHV STEM. It is shown that segregated Cu exists in a chemical environment similar to that of Cu atoms in bulk θ-phase precipitates.Films of 100 nm thickness and nominal composition Al-2.5wt%Cu were deposited by sputtering from alloy targets onto NaCl substrates. The samples were solution heat treated at 748K for 30 min and aged at 523K for 4 h to promote equilibrium grain boundary segregation. EELS measurements were made using a Gatan 666 PEELS spectrometer interfaced to a VG HB501 STEM operating at 100 keV. The probe size was estimated to be 1 nm FWHM. Grain boundaries with the narrowest projected width were chosen for analysis. EDX measurements of Cu segregation were made using a VG HB603 STEM.

Deformation Twins Formed in Nanocrystalline Materials

2006 ◽  
Vol 503-504 ◽  
pp. 125-132 ◽  
Author(s):  
Yuntian T. Zhu
Keyword(s):  
Grain Boundaries ◽  
Nanocrystalline Materials ◽  
Partial Dislocation ◽  
Room Temperature ◽  
High Pressure Torsion ◽  
Nucleation And Growth ◽  
Analytical Models ◽  
Partial Dislocations ◽  
Deformation Twins ◽  
Low Strain Rate

Deformation twins have been oberved in nanocrystalline (NC) Al synthsized by cryogenic ball-milling and in NC Cu processed by high-pressure torsion under room temperature and at a very low strain rate. They were found formed by partial dislocations emitted from grain boundaries. This paper first reviews experimental evidences on deformation twinning and partial dislocation emissions from grain boundaries, and then discusses recent analytical models on the nucleation and growth of deformation twins. These models are compared with experimental results to establish their validity and limitations.

A model of Fe3+-kaolinite, Al3+-goethite, Al3+-hematite equilibria in laterites

Clay Minerals ◽  
1989 ◽  
Vol 24 (1) ◽  
pp. 1-21 ◽  
Author(s):  
F. Trolard ◽  
Y. Tardy
Keyword(s):  
Stability Field ◽  
Equilibrium Conditions ◽  
Dissolved Silica ◽  
Silica Activity ◽  
Proposed Model ◽  
Coexisting Phases ◽  
Activity Temperature ◽  
The Stability ◽  
Fe Substitution ◽  
Mineral Constituents

AbstractThe distribution of Fe3+-kaolinite, Al-goethite and Al-hematite and their contents of Fe and Al in bauxites and ferricretes are controlled by water activity, dissolved silica activity, temperature and particle size. The proposed model, based on ideal solid-solution equilibria in the Fe2O3-Al2O3-SiO2-H2O system, takes into account water and silica activities. By using the same considerations as those previously developed for the Fe2O3-Al2O3-H2O system, the model calculates the amounts of coexisting phases, Al or Fe substitution ratios in goethite, hematite or kaolinite, and the stability field distributions of the minerals under various conditions. Thermodynamic equilibrium conditions and element distributions within the mineral constituents are shown to be dependent on the parameters cited above. The model yields results compatible with natural observations on lateritic profiles.

Role of Grain Boundary Segregation in Austenite Decomposition of Low-Alloyed Steel

2007 ◽  
Vol 558-559 ◽  
pp. 965-970 ◽  
Author(s):  
Shigeru Suzuki ◽  
M. Tanino
Keyword(s):  
Boron Nitride ◽  
Grain Boundaries ◽  
Boundary Segregation ◽  
Austenite Decomposition ◽  
Microstructure Observation ◽  
Austenite Grain ◽  
Auger Spectra ◽  
Low Alloyed Steel ◽  
Manganese Steels

The influence of addition of small amounts of boron and nitrogen on the microstructure formed by austenite decomposition in low-alloyed manganese steels was investigated. In order to understand microstructural changes by addition of boron and nitrogen, Auger electron spectroscopy was used for analyzing prior austenite grain boundaries in steels doped with phosphorus, boron and nitrogen. The results by microstructure observation showed that the formation of Widmanstätten ferrite was suppressed by addition of a small amount of boron in the steels, whereas Widmanstätten ferrite appears to be formed again by addition of boron and nitrogen. The Auger spectra showed that small particles of boron nitride were detected on grain boundaries in steel doped with boron and nitrogen, while boron was segregated at grain boundaries in steel with boron. This indicates that segregation of boron at grain boundaries and/or sub-boundaries may suppress the formation of Widmanstätten ferrite, while the formation of boron nitride seems to be ineffective to suppression of the formation of Widmanstätten ferrite in steels doped with boron and nitrogen.

What is Behind the Inverse Hall-Petch Behavior in Nanocrystalline Materials?

2006 ◽  
Vol 976 ◽  
Author(s):  
Christopher Carlton ◽  
P. J. Ferreira
Keyword(s):  
Grain Size ◽  
Yield Strength ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Nanocrystalline Materials ◽  
Critical Value ◽  
Petch Relationship ◽  
And Diffusion ◽  
Critical Grain Size

AbstractAn inverse Hall-Petch effect has been observed for nanocrystalline materials by a large number of researchers. This result implies that nanocrystalline materials get softer as grain size is reduced below a critical value. Postulated explanations for this behavior include dislocation based mechanisms and diffusion based mechanisms. In this paper, we report an explanation for the inverse Hall-Petch effect based on the statistical absorption of dislocations by grain boundaries, showing that the yield strength is both dependent on strain rate and temperature, and that it deviates from the Hall-Petch relationship at a critical grain size.

Atomic Scale Characterisation of Electrodeposited Nanocrystalline Ni-P Alloys

1999 ◽  
Vol 581 ◽  
Author(s):  
Matthias Abraham ◽  
Mattias Thuvandert ◽  
Helen M. Lane ◽  
Alfred Cerezo ◽  
George D.W. Smith
Keyword(s):  
Heat Treatment ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Three Dimensional ◽  
Boundary Segregation ◽  
Atom Probe ◽  
Atomic Scale ◽  
Grain Boundary Segregation ◽  
P Concentration

ABSTRACTNanocrystalline Ni-P alloys produced by electrodeposition have been characterised by three-dimensional atom probe (3DAP) analysis. In the as-deposited materials, there are indications of some variation in P concentration between grains and segregation to grain boundaries. After heat treatment however, strong grain boundary segregation and the formation of Ni3P precipitates have been observed.

Fracture Modes in Ll2 Compounds

1988 ◽  
Vol 133 ◽  
Author(s):  
C. L. Briant ◽  
A. I. Taub
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Intermetallic Compounds ◽  
Boundary Segregation ◽  
Grain Boundary Segregation ◽  
Fracture Modes ◽  
Beneficial Effects ◽  
Boron Segregation ◽  
Total Composition ◽  
Carbon Additions

ABSTRACTThis paper reports a study of grain boundary segregation and fracture modes in Ll2 intermetallic compounds. Data obtained on Ni3A1, Ni3Si, Ni3Ga, Ni3Ge, and Pt3Ga will be presented. It will be shown that the amount of boron segregation and its ability to improve cohesion depends on the total composition of the compound. The beneficial effects of boron can be counteracted by the presence of borides on the grain boundaries. Carbon additions also produce some improvement in ductility in Ni3Si.

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